1. Field of the Invention
The present invention relates to an image forming apparatus having an image reading portion and an image forming portion.
2. Related Background Art
There is a conventional image forming apparatus which provides space between an image reading portion and an image forming portion for stacking sheets with images formed thereon. FIG. 8 shows an example of the conventional apparatus. Such an apparatus does not need a tray for stacking sheets with images formed thereon to be provided on the side of the apparatus, which has the advantage of reducing the space the apparatus occupies.
In FIG. 8, an apparatus main body Axe2x80x2 of an image forming apparatus 2200 is provided with an image reading portion Bxe2x80x2 on the upper side and an image forming portion Cxe2x80x2 on the lower side. The image reading portion Bxe2x80x2 functions as image reading means for reading image information of a book original, while the image forming portion Cxe2x80x2 functions as image forming means. A sheet deck Dxe2x80x2 is attached underneath the image forming portion Cxe2x80x2 so that the image forming portion Cxe2x80x2 and the sheet deck Dxe2x80x2 will constitute an image forming section.
The image reading portion Bxe2x80x2 is constituted of a scanning system light source 2201, a platen glass plate 2202, an original pressure plate 2203 capable of opening and closing a scanning main body Exe2x80x2, a mirror 2204, a lens 2205, a light receiving element (photoelectric element) 2206, an image processing portion and so on.
Sheets with toner images formed thereon by the image forming portion Cxe2x80x2 are stacked on a delivery portion 2120 arranged inside the apparatus (this type of delivery method is referred to below as in-body delivery).
For the in-body delivery system, some frame structures are known to provide a space between the image reading portion and the image forming portion. For example, Japanese patent application laid-open No. 5-197225 describes an image forming apparatus (see FIG. 9) in which the image reading portion is supported at two corners (301, 302) on the rear side of a sheet removing portion 300. Japanese patent No. 2685458 describes an image forming apparatus (see FIG. 10) in which the image reading portion is supported at two corners (401, 402) on the diagonal line with respect to the top of the image forming portion. Japanese patent application laid-open No. 8-340414 describes an image forming apparatus (see FIG. 11) in which a scanner part is supported at four corners (501, 502, 503, 504) on the top of a printer part.
The above-mentioned frame structures, however, have respective drawbacks. For example, the apparatus (FIG. 9) described in Japanese patent application laid-open No. 5-197225 is such that columns are provided in two positions (at two corners) alone. Therefore, when the pressure plate and the like of the image reading portion is strongly pressed from above against a thick book or the like as an original, the columns supporting the image reading portion may be deformed plastically. On the other hand, the apparatus (FIG. 11) described in Japanese patent application laid-open No. 8-340414 is restricted to removing sheets only from the front side. Therefore, when printing on A3 sheets or longer or when removing narrower sheets from the in-body delivery portion, an operator has to stoop over his or her work, which puts a load on the operator.
To solve the above-mentioned problems, there is still another type of apparatus 600 as shown in FIG. 12. The apparatus 600 provides a space only in the front left-hand corner 601 of the apparatus, which makes them possible to prevent plastic deformation of the columns and increase the removability of paper.
The apparatus of FIG. 12 is such that the frame of the original reading portion and built-in components of the frame, namely a first mirror unit (first scanning optical system) 631 and second mirror units (second scanning optical systems) 632 and 633, are supported on three points. In other words, only three columns provided at three corners of the frame support the frame and the built-in components. Therefore, when pushed down from above, the frame is distorted or deformed as shown in FIG. 12 from the solid-line position to the dot and dash line position, which in turn makes it easy to deform rail planes that essentially lead the optical systems into operation in accordance with the deformation. As a result, as shown in FIG. 13A, an optical path (which assumes end points c and d) indicated by the dot and dash line is formed on the rear side of the mirror units, while an optical path (which assumes end points a and b) indicated by the solid line is formed on the front side. FIG. 13B illustrates both optical paths three-dimensionally.
If the optical paths, which are expected to be essentially parallel with each other, are mutually twisted, a right-angled aberration (distortion) occurs to an output image (FIG. 14B), compared to an ideal output image (FIG. 14A). This makes it difficult to sufficiently ensure the accuracy of image formation.
It is an object of the present invention to prevent optical paths from being distorted in an image forming apparatus even if an image reading portion is deflected, the image reading portion being provided separately from an image forming portion so that recording media will be delivered between the image reading portion and the image forming portion.
It is another object of the present invention to provide an image forming apparatus comprising: a reader portion for reading an original image, the reader portion including an original placement stand on which an original is placed and a scanning unit for scanning the original on the original placement stand from a predetermined home position at which the scanning unit is at rest during each non-scan period; an image forming portion for forming an image on a recording sheet according to an image signal; and a delivery portion provided between the reader portion and the image forming portion for delivering the recording sheet with the image formed thereon by the image forming portion, wherein the reader portion is supported by the image forming portion in the general shape of a letter xe2x80x9cLxe2x80x9d at least on the home position side and the rear side of the apparatus.
Other objects of the present invention will become apparent from the following description of an embodiment with reference to the accompanying drawings.